This is a Shannon Award providing partial support for the research projects that fall short of the assigned institute's funding range but are in the margin of excellence. The Shannon Award is intended to provide support to test the feasibility of the approach; develop further tests and refine research techniques; perform secondary analysis of available data sets; or conduct discrete projects that can demonstrate the PI's research capabilities or lend additional weight to an already meritorious application. The abstract below is taken from the original document submitted by the principal investigator. The facultative gram-negative bacterium, Actinobacillus actinomycetemcomitans, has been recognized as an important pathogen in various forms of periodontal disease. The role of this bacterium in localized juvenile periodontitis (LJP) has been the subject of intense investigation. More recently, molecular approaches such as DNA fingerprinting and restriction fragment length polymorphism (RFLP) analysis have been used to learn about the transmission and epidemiology of this bacterium in LJP. In this proposal, the hypothesis that a subset of human isolates of A. actinomycetemcomitans that are associated with LJP are clonal will be tested. The study of the genetic variability and clonality of defined populations of A. actinomycetemcomitans will facilitate the identification of specific clonal types of the bacterium that have the potential to be virulent or relatively avirulent. The specific aims of the project are: (1) To determine the genetic variation of natural populations of A. actinomycetemcomitans in LJP. Multilocus enzyme electrophoresis and arbitrarily primed polymerase chain reaction will be used to determine the clonality of the bacterial species in a well-characterized collection of clinical isolates from LJP families. Clonal lines identified by these methods will be compared to genotypic groups previously characterized by RFLP. The objective is to establish that certain clonal types of A. actinomycetemcomitans correlate with the onset of LJP. (2) To characterize differences in the organization of putative virulence genes among members of those clonal types of A. actinomycetemcomitans associated with a disease and healthy periodontal status. RFLP analysis will be used to determine if genetic heterogeneity in a leukotoxin operon correlates with the distribution of specific clonal types in cases of disease and health. If this is the case, differences in gene expression can be related to the pathogenic potential of individual clones. (3) To assess clonal variability in the structure of specific cell surface components of A. actinomycetemcomitans. The objective is to determine if those clonal types of A. actinomycetemcomitans that are associated with a diseased periodontal status express unique molecular species of lipopolysaccharide (LPS) and the major outer membrane proteins. Particular emphasis will be placed on detecting structural differences in the major outer membrane protein that functions as an immunoglobulin Fc receptor. Clonal differences in these cell surface components, as in the case of the leukotoxin, would support the concept that virulent and avirulent variants or strains of A. actinomycetemcomitans exist in the human oral flora. Thus, the information obtained in this study will lead to the identification of bacterial "strains" and products that should serve as the most appropriate subjects for studies that focus on epidemiology, diagnostics, pathogenicity and host immune response in periodontal disease research.